In the manufacture of a semiconductor device, a process of filling a semiconductor material such as silicon or the like into a depression such as a hole or a trench formed on a surface of a semiconductor wafer may be performed. The semiconductor wafer includes a semiconductor substrate and an insulating film formed on the semiconductor substrate. The depression is formed in the surface of the insulating film (the surface of the semiconductor wafer). The semiconductor material filled into the depression is the same as the material of the semiconductor substrate and is often used as, e.g., an electrode.
In the related art, there is known a method and apparatus for filling a depression formed in an insulating film of a workpiece which is a semiconductor wafer. The depression filling method includes a step of forming a first amorphous silicon film containing an impurity along a wall surface which defines a depression, a step of forming a second amorphous silicon film on the first amorphous silicon film, and a step of annealing the workpiece after the second amorphous silicon film is formed.
A depression provided on a surface of a semiconductor wafer may be formed so as to pass through the insulating film and extend up to an inside portion of a semiconductor substrate which serves as abase of the insulating film. This depression is formed by etching the insulating film and the semiconductor substrate. The present inventors have been studying a technique in which a depression is filled by moving a semiconductor material toward the bottom portion of the depression and forming an epitaxial region conforming to crystals of a semiconductor substrate from the semiconductor material.
A semiconductor material is deposited on a sidewall and a bottom wall of a depression so as not to occlude the depression and then solid phase epitaxial growth is performed with respect to the semiconductor material, so that an epitaxial region is formed in the depression. By repeatedly performing the step of forming the epitaxial region, the epitaxial region is expanded in the depression. In the case where an impurity is not contained in the semiconductor material, addition of an impurity to the epitaxial region can be performed by gas phase doping. If epitaxial growth from the semiconductor material is further performed at a subsequent step on the surface of the epitaxial region to which the impurity is added by the gas phase doping, the impurity already added by the gas phase doping at the step which precedes this step is contained in the epitaxial region formed until this step. The epitaxial region containing an impurity is higher in etching rate than the epitaxial region not containing an impurity. Thus, when the semiconductor material left on the sidewall without undergoing epitaxial growth is removed by etching after the formation of the epitaxial region, there is a possibility that damage attributable to the etching is generated even in the epitaxial region. Accordingly, in the technique of filling a depression by epitaxial growth of a semiconductor material, it is necessary to reduce the influence of etching on an epitaxial region filled into a depression.